Method for operating a rotational-speed-variable refrigerant compressor

ABSTRACT

The invention relates to a method for operating a rotational-speed-variable refrigerant compressor (2) for cooling a cooling volume (4) of a refrigeration system (1), which refrigeration system does not have its own control unit, wherein the refrigeration system (1) comprises at least one thermostat (3) for directly or indirectly monitoring a temperature state of the cooling volume (4) and wherein the rotational-speed behavior of the refrigerant compressor (2) during a cooling cycle is controlled by means of a specification rotational-speed control stored in an electronic control device (6) of the refrigerant compressor (2). According to the invention, in order to enable adjustment of the rotational-speed behavior in reaction to a preceding special operating state and to enable energy-optimized cooling of the cooling volume (4) that is as fast as possible, at least one comparison parameter is stored in the electronic control device (6) of the refrigerant compressor (2) and exceedance or undershooting of the comparison parameter by a current measured parameter value is monitored, a special cooling cycle different from the specification rotational-speed control is triggered if the current measured parameter value exceeds or undershoots the comparison parameter, possibly, a current cooling cycle controlled by means of the specification rotational-speed control is interrupted by the special cooling cycle.

FIELD OF THE INVENTION

The invention concerns a method for operating a refrigerant compressorhaving a variable rotary speed for cooling a cooled volume of arefrigeration system, wherein the refrigeration system comprises atleast one thermostat for direct or indirect monitoring of a temperaturestate of the cooled volume and wherein the refrigerant compressor isoperated cyclically and a cooling cycle of the refrigerant compressorbegins when the refrigerant compressor is set to an ON state by aswitching signal triggered by the thermostat, and the cooling cycle endswhen the refrigerant compressor is set to an OFF state by anotherswitching signal triggered by the thermostat, wherein an operating cyclecomprises, in addition to the cooling cycle, a rest cycle that followsthe cooling cycle, and wherein the rotary speed behavior of therefrigerant compressor is controlled during a cooling cycle by means ofa preset rotary speed control that is stored in an electronic controldevice of the refrigerant compressor; and an electronic control devicefor controlling the cyclic operation of a variable-speed refrigerantcompressor. The electronic control device of the refrigerant compressoris frequently also called the electronic control and regulation deviceof the refrigerant compressor.

Preferably, the rotary speed behavior of the refrigerant compressorduring a cooling cycle is controlled on the basis of at least onepredefined parameter by means of a preset rotary speed control stored inan electronic control device of the refrigerant compressor, bymonitoring the at least one predefined parameter with regard to acurrent parameter of a current cooling cycle exceeding and/or fallingshort of it.

Variable-speed refrigerant compressors can be used in connection withmany various refrigeration systems and refrigeration equipment, thus,for example, refrigerators or refrigerated display cases, freezers, airconditioners, or heat pumps. They offer the advantage over fixed-speedrefrigerant compressors that they are able to operate in an energyoptimized way and can adjust the delivered cooling output to the coolingrequirement relative to the cooled volume.

Optimally, variable-speed refrigerant compressors are used inrefrigerant systems that have their own electronic control device andcomponents for monitoring the operating state of the refrigerantsystems. As a consequence, such refrigerant systems are called smartrefrigerant systems. In this case, various switching signals,parameters, and measurements are processed in the electronic controlunit of the refrigeration system, which is different from the electroniccontrol device of the refrigerant compressor, and a control signal isgenerated from said input parameters and transmitted to the electroniccontrol device of the refrigerant compressor. This control signal can,for example, be a rotary speed setting, which, depending on the currenttemperature or the path of the temperature of the cooled volume, tellsthe electronic control device of the refrigerant compressor the rotaryspeed with which the refrigerant compressor is to be operated, or if theelectronic control device of the refrigerant compressor is to turn it onor off.

Therefore, the operation, in particular the rotary speed behavior of avariable-speed refrigerant compressor, is controlled in smartrefrigerant systems by the interplay of the electronic control unit ofthe refrigeration system with the electronic control device of therefrigerant compressor, wherein the electronic control unit of therefrigeration system as a rule sends already specified refrigerationrequirements to the electronic control device of the refrigerantcompressor.

The current invention, however, concerns a different kind ofrefrigeration system, namely ones that do not have an electronic controlunit that can communicate with the electronic control device of therefrigerant compressor and that do not have electronic components formonitoring the operating state of the refrigeration system. Suchrefrigeration systems therefore are called simple refrigeration systemsin what follows. They comprise at least one thermostat, which monitorsthe temperature state of the cooled volume and, depending on the currenttemperature state, triggers a switching signal that sets the refrigerantcompressor to the ON state or sets it to the OFF state. Simplerefrigeration systems do not communicate a rotary speed setting to theelectronic control device of the refrigerant compressor or any otherdata. They are also not capable of recording other operating parameterssuch as the temperature of the cooled space or the path of thetemperature and calculating the refrigeration requirements on therefrigerant compressor from them.

Cooling output is either demanded or not demanded by the thermostat, butwithout quantifying it, i.e., the rotary speed regulation of therefrigerant compressor is solely undertaken by the electronic controldevice of the refrigerant compressor, thus by its programming.

In order to nevertheless be able to use the fundamental advantage ofvariable-speed refrigerant compressors over fixed-speed refrigerantcompressors, it is necessary that the rotary speed behavior of therefrigerant compressor controlled by the electronic control device ofthe refrigerant compressor be as optimized as possible with respect to adefined parameter, for example with respect to energy consumption.

“As energy optimized as possible” is in this case to be understood tomean that the current consumption or energy consumption of therefrigerant compressor is particularly low at the cooling of the cooledvolume required for the relevant application and the refrigerantcompressor therefore can be operated in a resource-conserving way.

The fact that the electronic control device of the refrigerantcompressor does not obtain any information from the refrigeration systemabout its operating state, in particular it does not receive a rotaryspeed setting, is seen as a complicating factor here.

This disadvantage is compensated in practice by the fact that simplerefrigeration systems are characterized by having a lower purchase pricethan smart refrigeration systems, due to which they are neverthelessvery popular worldwide.

PRIOR ART

Both variable-speed and fixed-speed refrigerant compressors produce acirculation of a refrigerant in a closed refrigerant system. Therefrigerant becomes heated by absorption of energy from the cooledvolume in an evaporator and in the end becomes superheated and is pumpedto a higher pressure by a piston moving back and forth in a cylinderhousing in a piston-cylinder unit, wherein the refrigerant releases heatvia a condenser and is transported back to the evaporator via a choke,in which a reduction of pressure and cooling of the refrigerant takesplace. The movement of the piston is implemented via a crank mechanismcomprising a crankshaft that is driven by an electric drive unit.

The refrigeration process described above runs during a cooling cycle ofthe refrigerant compressor, wherein the refrigerant compressor is drivenduring the cooling cycle and has a rotary speed behavior controlled bythe electronic control device of the refrigerant compressor, wherein theelectronic control device controls the electric drive unit of therefrigerant compressor.

A cooling cycle starts via a switching signal triggered by thethermostat of the refrigeration system, which sets the refrigerantcompressor to the ON state. For example, the thermostat triggers aswitching signal for the ON state of the refrigerant compressor when thetemperature level in the cooled volume or a cooled volume temperature ora temperature representative of the cooled volume temperature exceeds apreset maximum value. For purposes of monitoring the temperature stateof the cooled volume, the thermostat can, for example, be made as avapor pressure-based thermostat, in particular as a bellows thermostat,or can have a bimetallic strip or an NTC (negative temperaturecoefficient) element as temperature sensor.

The refrigerant compressor is driven or remains in the cooling cycle, inwhich the refrigeration process takes place, until the electroniccontrol unit of the refrigerant compressor receives another switchingsignal triggered by the thermostat, which sets the refrigerantcompressor to the OFF state. Said signal in this case can be triggered,for example, when the temperature level or a cooled volume temperatureor a temperature representative of the cooled volume temperature hasfallen below a preset minimum value because of cooling in the cooledvolume that has taken place in the cooling cycle.

In order to enable the cooling of the cooled volume to be as energyoptimized as possible, the electronic control device of the refrigerantcompressor operates according to a programmed specification during thecooling cycle, which controls the rotary speed behavior of therefrigerant compressor during a cooling cycle. This preset rotary speedcontrol enables variable-speed refrigerant compressors to be controlledindividually, or energy optimized, within the scope of the programmedspecification even in simple refrigeration systems, which, as notedabove, do not themselves have an electronic control unit that is capableof communicating with the electronic control device of the refrigerantcompressor.

The preset rotary speed control is set so that at least one currentparameter that can be detected by the electronic control of therefrigerant compressor during a cooling cycle is compared with at leastone predefined parameter stored in the electronic control device and therotary speed behavior of the refrigerant compressor is controlled independence on it. In other words, the refrigerant compressor iscontrolled by means of the preset rotary speed control stored in theelectronic control device on the basis of at least one predefinedparameter, by monitoring the at least one predefined parameter withregard to a current parameter of a current cooling cycle exceeding orfalling short of it.

The at least one predefined parameter can involve various parameters,for example the electric load of the refrigerant compressor, which isdetermined by measuring the electric current through the refrigerantcompressor, in particular the electric current flowing through theelectric drive unit of the refrigerant compressor during the coolingcycle.

More preferably, however, the predefined parameter is the duration of acooling cycle. The predefined parameter in this case stands for thevalue of the parameter at which a cyclic operation that is as energyoptimized as possible is enabled for a preset rotary speed behaviorduring a cooling cycle, preferably at as low as possible a rotary speedat which the electric motor driving the refrigerant compressor can beoperated with high efficiency.

In other words, a temperature level in the cooled volume of therefrigeration system is to be permanently kept as energy optimized aspossible by the preset rotary speed control. If the duration of acooling cycle is the predefined parameter, the preset rotary speedcontrol causes the electronic control device of the refrigerantcompressor to change its rotary speed either immediately or in the nextcycle if the preset duration is exceeded or not reached, thus if thetime between the demand of the thermostat of the simple refrigerationsystem to switch the refrigerant compressor on or off is longer orshorter than the predefined parameter, with the goal of subsequentcooling cycles again having a duration that corresponds to thepredefined parameter (duration), so that the refrigerant compressor canagain be operated as energy optimized as possible in every coolingcycle.

Such a preset rotary speed control for operation of a variable-speedrefrigerant compressor in a simple refrigeration system is known, forexample, from DE 1092013114374. In this case, the control of the rotaryspeed behavior takes place either during the current cooling cycle,wherein the rotary speed of the refrigerant compressor is increased ifit was detected that the current parameter exceeded the at least onepredefined parameter (the duration of a cooling cycle in that patent).Such an increase can also take place several times during a coolingcycle if the current parameter exceeds a plurality of predefinedparameters, i.e., if, for example, in spite of increasing the rotaryspeed the thermostat still does not initiate a switching signal toswitch off the refrigerant compressor, because the temperature level ora cooled volume temperature or a temperature representative of thecooled volume temperature in the cooled volume is still too high.

The increase can take place, for example, progressively, regressively,linearly, or stepwise.

If the electronic control unit detects, for example after multiplecooling cycles of the refrigerant compressor, that the, also multiple,increases of the rotary speed in each cooling cycle still does notresult in the predefined parameter, for example the predefined durationof a cooling cycle, being able to be maintained, then it can also beprovided according to the prior art that the starting rotary speed ofone or more subsequent cooling cycles will already be set to be higherthan is envisaged in the energy optimized case.

It can equally be provided that the starting rotary speed of asubsequent cooling cycle is reduced if the at least one predefinedparameter is not reached.

How accurately the rotary speed behavior of the refrigerant compressoris represented on the basis of the preset rotary speed control isdependent on the individual programming that is provided by therefrigerant compressor manufacturer upon delivery of the refrigerantcompressor. In any case, it is important that the preset rotary speedcontrol, which controls the rotary speed during a cooling cycle, takesplace as a function of a predefined parameter.

The at least one predefined parameter is selected by the manufacturer ofthe refrigerant compressor so that known operating parameters of therefrigeration system such as heat or cold losses in the cooled volumeand/or in the refrigerant system and possibly expected ambienttemperatures are taken into account, so that the variable-speedrefrigerant compressor runs as energy optimized as possible during thecooling cycle due to the preset rotary speed control. If there aredeviations of a current parameter corresponding to at least onepredefined parameter from the at least one predefined parameter during acurrent cooling cycle, the preset rotary speed control serves to controlthe rotary speed behavior of the refrigerant compressor so that thecurrent parameter essentially again corresponds to the predefinedparameter as quickly as possible, either during the current coolingcycle or at least in a subsequent cooling cycle or within a fewsubsequent cooling cycles.

A disadvantage of the control of the prior art lies in the fact that theelectronic control device of the refrigerant compressor is not capableof reacting to any special operating states such as an increased coolingdemand after a defrost operation or after a power outage. These specialoperating states and the problems connected with them are brieflydescribed below.

Even simple refrigeration systems run a defrost operation at certaintime intervals, wherein the area around the evaporator is heated duringa defrost operation, for example by heating elements, so as to remove ordefrost ice or frost deposits that have built up in the vicinity of theevaporator in the cooled volume of the refrigeration system. Thisensures maintenance of an efficient cooling of the cooled volume, sincethe ice or frost deposits, in particular if they have built up a solidlayer, act as an insulating layer and prevent the exchange of heatbetween the cooled volume and the evaporator. The refrigerant that is inthe evaporator unavoidably becomes heated during the defrost operation.

Simple refrigeration systems in this case are controlled as a rule sothat a timer initiates a defrost operation at periodic intervals,provided the refrigerant compressor was set into the OFF state due tothe further switching signal triggered by the thermostat. During thedefrost operation, the thermostat does not trigger a switching signal toset the refrigerant compressor to the ON state, so that the refrigerantcompressor remains in the OFF state during the defrost operation. Whenthe defrost operation is over, the switching signal is triggered by thethermostat because of the deviation of the temperature level in thecooled volume or the cooled volume temperature or the temperaturerepresentative of the cooled volume temperature detected due to theheating of the evaporator and the refrigerant compressor starts acooling cycle in accordance with the preset rotary speed control.

Another problem in simple refrigeration systems results from the factthat simple refrigeration systems are often operated in regions withweak infrastructure, in which a steady supply of electricity is notguaranteed, rather interruptions of the electricity supply are the orderof the day. In each case according to the duration of the power outage,the temperature in the cooled volume rises. As soon as the power supplyis restored, the switching signal is triggered by the thermostat and therefrigerant compressor starts a cooling cycle in accordance with thepreset rotary speed control.

Since simple refrigerant compressors [sic; systems] themselves do nothave an electronic control unit that is capable of communicating withthe electronic control device of the refrigerant compressor, a coolingcycle in which the rotary speed is controlled in accordance with thepreset rotary speed control is triggered in the electronic controldevice of the refrigerant compressor in both special operating states,thus after the end of a defrost operation and after a power outage. Thisresults in the rotary speed of the refrigerant compressor beingincreased stepwise, thus the available cooling output rises slowly, eventhough the cooling demand for cooling the cooled volume is considerablyhigher after the defrost operation or because of the warming as aconsequence of the power outage than in the case of a normaloperation-related increase of the cooling demand, for which the presetrotary speed control is designed. This results in the length of thecooling cycle that follows the special operating state beingdisproportionately higher than the duration of the preceding coolingcycles and an increased energy consumption of the refrigerant compressorresulting from the long duration of the cooling cycle.

OBJECT OF THE INVENTION

Therefore, it is an object of the invention to overcome thedisadvantages of the prior art and to propose a method for operating avariable-speed refrigerant compressor having an electronic controldevice so that in the operation of such a variable-speed refrigerantcompressor with a simple refrigeration system, which does not have itsown electronic control unit that can communicate with the electroniccontrol device of the refrigerant compressor, which method enables anadjustment of the rotary speed behavior in reaction to a specialoperating state that has occurred, in order to lower the cooled spacetemperature as quickly as possible and as energy-optimized as possible.

DESCRIPTION OF THE INVENTION

The invention concerns a method for operating a variable-speedrefrigerant compressor as a part of a simple refrigeration system thatdoes not have its own control unit, of the kind mentioned at the start.

In order to detect, in the electronic control device of the refrigerantcompressor, a special operating state of the refrigeration system thathas occurred, it is provided according to the invention that at leastone comparison parameter is stored in the electronic control device ofthe refrigerant compressor, and an exceeding or falling short of thecomparison parameter by a current measured parameter value is monitored.While the monitoring of the at least one characteristic parameter in thepreset rotary speed control is aimed only at a normal operation of therefrigerant compressor and is aimed for an operation of the refrigerantcompressor that is as energy optimized as possible during such a normaloperation, the monitoring of the comparison parameter is designed todetect a special operating state of the refrigeration system that hasoccurred, in particular a defrost operation or a power outage, andtherefore represents a second monitoring state that is separate from themonitoring state necessary for the preset rotary speed control. However,it is conceivable that the at least one comparison parameter is the samemeasured parameter as in the case of the at least one parameter, but themeasured parameter is monitored in different methods.

When the comparison parameter and the characteristic parameter are thesame measured parameter, it is necessary that the specificallyestablished values or value ranges of the comparison parameter andcharacteristic parameter differ from each other. In particular, it canbe provided that the comparison parameter is a value of the measuredparameter that is not associated with the normal operation or at whichthe normal operation is no longer the optimum operating state, since,for example, the required cooling capacity can no longer be madeavailable by means of the preset rotary speed control. In other words,the comparison parameter can be a value of the measured parameter thatlies outside of the normal operation controlled by means of the presetrotary speed control.

The at least one comparison parameter is a quantity that the electroniccontrol device of the refrigerant compressor can detect and monitoritself without being dependent on additional data from a control unit ofthe refrigeration system, which is not present in simple refrigerationsystems. The duration of the operating cycles of the refrigerantcompressor, in particular the cooling cycle and rest cycle, and also theload of the refrigerant compressor measured as the current of therefrigerant compressor or another temperature that is independent of thetemperature of the cooled volume are in this case conceivable as the atleast one comparison parameter. The monitoring of two or three differentcomparison parameters, for example thus the load and duration of anoperating cycle or the load and/or duration of an operating cycle and anadditional temperature, is also conceivable, wherein the at least onecomparison parameter in this case comprises two or three comparisonparameters, each of which represent different measured quantities.

This also applies correspondingly to the relevant current measuredparameter value, which in each case is associated with a comparisonparameter and correspondingly refers to the same measured quantity asthe associated comparison parameter, in order to be able to detect anexceeding or falling short of the comparison parameter or the value ofthe comparison parameter. In other words, the current parameter value isa currently measured value of the measured quantity, which can becompared with the comparison parameter.

The comparison parameter in this case can be stored in the electroniccontrol unit as a preset value, thus already defined by themanufacturer, but can also be redetermined continuously in operation, inorder to enable the detection of the defrost operation as a departurefrom the preset rotary speed control, as described below in more detail.The value of the at least one comparison parameter is in this case alimit value, which is set so that if the comparison parameter isexceeded or fallen short of by the current parameter value, an inferencecan be made with respect to a special operating state that has occurred,in particular a defrost operation or a power outage.

As soon as a preceding special operating state has been detected, therefrigerant compressor is operated with a special cooling cycle that isdifferent from the preset rotary speed control in order to be able toadjust the rotary speed behavior of the refrigerant compressor to theeffects of the special operating state and possibly to send a highcooling output to the cooled volume after the detection of the specialoperating state. This is why it is provided according to the inventionthat a special cooling cycle that is different from the preset rotaryspeed control is triggered when the currently measured parameter valueexceeds or falls short of the comparison parameter. The detection of thespecial operating state can take place at any time point in theoperating cycle, for example during the rest cycle, directly at thestart of a cooling cycle, or during a cooling cycle, in each caseaccording to which comparison parameter is being monitored. For example,it can be provided in the case of a detection that has taken placeduring the rest cycle or at the start of the cooling cycle that thespecial cooling cycle is started instead of an originally intendedstandard cooling cycle. In this case, the switching signal triggered bythe thermostat, which sets the refrigerant compressor to the ON state,triggers the special cooling cycle. If the detection of the specialoperating state takes place during a cooling cycle, the cooling cycle isinterrupted and the special cooling cycle is started.

As a rule, the special cooling cycle is characterized by a rotary speedbehavior having an average rotary speed that is higher than the averagerotary speed of the preset rotary speed control. An increased coolingoutput of the refrigerant compressor results directly from the increaseof the average rotary speed. Here, the average rotary speed means therotary speed averaged over the duration of the cooling cycle, forinstance as the arithmetic, geometric, or harmonic average.

Therefore, the object stated above is solved for a simple refrigerationsystem in a method according to the invention of the kind described atthe start in that

-   -   at least one comparison parameter is stored in the electronic        control device of the refrigerant compressor and an exceeding or        falling short of the comparison parameter by a current measured        parameter value is monitored,    -   a special cooling cycle that is different from the preset rotary        speed control is initiated if the current measured parameter        value exceeds or falls short of the comparison parameter,    -   optionally, a current cooling cycle controlled by the preset        rotary speed control is interrupted by the special cooling        cycle.

Analogously, the invention also concerns an electronic control devicefor control of the cyclic operation of a variable-speed refrigerantcompressor, wherein the electronic control device is configured

-   -   to switch on a switching signal triggered by a thermostat for        direct or indirect monitoring of a temperature state of a cooled        volume of a refrigeration system in order to begin a cooling        cycle and to end a rest cycle and    -   to switch off again an additional switching signal triggered by        the thermostat in order to end the cooling cycle and to begin a        rest cycle and    -   to control the rotary speed behavior of the refrigerant        compressor during a cooling cycle by means of a preset rotary        speed control stored in the electronic control device.

The object stated at the start is solved in this case in that at leastone comparison parameter is stored in the electronic control device andthe electronic control device is configured

-   -   to detect an exceeding or falling short of the comparison        parameter by a current measured parameter value,    -   to initiate a special cooling cycle that is different from the        preset rotary speed control when the current measured parameter        value exceeds or falls short of the comparison parameter,    -   optionally, to interrupt a current cooling cycle controlled by        the preset rotary speed control in order to begin the special        cooling cycle.

In an embodiment of the method according to the invention it is providedthat the at least one monitored comparison parameter is a load of therefrigerant compressor in a starting phase of a cooling cycle. On theone hand, the load of the refrigerant compressor is suitable as anoperating parameter, since it can easily be detected by measuring theelectric current through the refrigerant compressor, in particularthrough the electric current flowing through the electric drive unit ofthe refrigerant compressor during the cooling cycle. The starting phaseof the cooling cycle begins as soon as the refrigerant compressor hasbeen set to the ON state due to reception of the switching signaltriggered by the thermostat.

The principle will be briefly explained using a preceding defrostoperation as an example: Because of the heating of the refrigerant inthe evaporator during the defrost operation or because of the highcooling demand, the load of the refrigerant compressor is especiallyhigh after a preceding defrost operation. If the currently measured loadtherefore exceeds the comparison value of the load that has been storedas comparison parameter, the electronic control device of therefrigerant compressor will infer that a defrost operation has takenplace and the special cooling cycle will be started. As a rule, acurrent cooling cycle will be interrupted in order to start the specialcooling cycle, thus, in other words, the preset rotary speed controlwill be switched off in order to be able to conduct the special coolingcycle. The electronic control device of the refrigerant compressor inthis case comprises switches or electronic components via which the atleast one operating parameter can be determined or measured.

Similarly, it is also provided in an embodiment of the electroniccontrol device according to the invention that the electronic controldevice is configured to measure a load of the refrigerant compressor asthe current through the refrigerant compressor and that the storedcomparison parameter and the currently measured parameter value areloads.

If the monitored comparison parameter is the load, it is advantageousnot to set a specific value of the load as comparison parameter, sincethe danger of an error detection would be elevated. Rather, it ispurposeful to employ an average load, which is measured over a definedstarting phase of the refrigerant compressor. The average load in thiscase is understood to be the average value of the loads, thus the sum ofall detected individual loads measured during the starting phase, forexample as arithmetic, geometric, or harmonic averages, over theduration of the starting phase. In this way, individual outliers of theload value can be neglected and a load behavior can be modelled. Inaddition, the preceding special operating state can be better monitoredwhile monitoring the average load, since because of the heating of therefrigerant in the refrigeration system, the load of the refrigerantcompressor over the starting phase of the cooling cycle, as a rule atleast over the first 30 s of the cooling cycle, is relatively high.Therefore, in another embodiment of the method according to theinvention it is provided that the load is monitored as the average loadmeasured over the duration of the start phase, wherein the duration ofthe start phase is preferably between 10 s and 90 s, in particularbetween 30 s and 80 s, especially preferably between 40 s and 70 s.

The duration of the rest cycle is also especially suitable as comparisonparameter, since during the normal operation according to the presetrotary speed control, the duration of the rest cycle does not as a ruleexceed a maximum value. Therefore, in another embodiment of the methodaccording to the invention it is provided that the at least onemonitored comparison parameter is a duration of the rest cycle. In otherwords, because of the cooling losses and/or insulation losses in thecooled volume, a duration is set, within which the target temperaturestate of the cooled volume is again exceeded after the end of thecooling cycle and thus the next cooling cycle is initiated. As a rule,however, the special operating state leads to a longer duration of therest cycle, for example up to 15 minutes. If the monitored operatingparameter is the duration of the rest cycle, the comparison parameter isdefined, for example, as the maximum value of the duration of the restcycle. If the actual duration of the current rest cycle exceeds thecomparison parameter, the electronic control unit will infer from thisdeviation that the refrigeration system is conducting a defrostoperation. Therefore, upon input of the next switching signal triggeredby the thermostat, the special cooling cycle can immediately be started.Of course, it is conceivable that both the load and the duration of therest cycle are monitored by the electronic control device and thespecial cooling cycle is initiated when, at least from the monitoring ofone of the two monitored parameters, preferably both of the monitoredparameters, a preceding defrost operation is inferred and the specialcooling cycle is initiated.

Similarly, it is also provided in an embodiment of the electroniccontrol device according to the invention that the electronic controldevice is configured to determine a duration of the rest cycle and thatthe stored comparison parameter and the currently measured parametervalue are the duration of a rest cycle.

In particular to detect an interruption of the power supply as apreceding special operating state, it is provided in a preferredembodiment of the invention that

-   -   an additional temperature independent of the temperature of the        cooled volume is measured,    -   the currently measured parameter value is the additional        temperature,    -   the at least one monitored comparison parameter is a comparison        temperature.

The detection and averaging of the additional temperature, which isindependent of the temperature level of the refrigerant compressormonitored by the thermostat, represents information in addition to theswitching signals of the thermostat for the electronic control device ofthe refrigerant compressor. As a result, the additional temperature ismeasured by a temperature measuring device, which is a component of theelectronic control device of the refrigerant compressor or is disposedon a housing of the refrigerant compressor. Thus, the additionaltemperature provides an inference about the operating temperature of theelectronic control device of the refrigerant compressor. By comparingthe currently measured additional temperature as the currently measuredparameter value and the comparison temperature as comparison parameter,it is possible, for example, to establish that the refrigerantcompressor was not in operation over a long period of time if thecurrently measured additional temperature is above the comparisontemperature. Thus, the monitoring of the additional temperature canindicate a previous special operating state, thus a defrost operation ora power outage.

Similarly, in another preferred embodiment of the electronic controldevice according to the invention it is provided that the electroniccontrol device is connected to a temperature measuring device to measurean additional temperature that is independent of the temperature of thecooled volume and that the stored comparison parameter is a comparisontemperature and the currently measured parameter value is the additionaltemperature. The temperature measuring device can be, for example, madeas a measurement probe, a resistance thermometer, a thermoelement, or atemperature sensor.

Normally, electronic control devices are capable of establishing apreceding power outage. However, they are not able to determine how longthe power supply was interrupted. If the outage was short, it would notbe purposeful to initiate a special cooling cycle, since only a smalladditional cooling demand exists in the cooled volume. Therefore, aspecial cooling cycle is only initiated if the electronic control deviceof the refrigerant compressor has established a power outage and thecomparison parameter is exceeded or fallen short of by the currentlymeasured parameter value. In this way, it can be ensured that thespecial cooling cycle is only initiated when an interruption of thepower supply has been established and it has been verified on the basisof the exceeding or falling short of the comparison parameter by thecurrently measured parameter value that indeed an elevated coolingdemand exists in the cooled volume.

Preferably, either the load, especially the average load, or theadditional temperature is employed as the currently measured parametervalue for the inference of a power outage, wherein the comparisonparameter is likewise a load, in particular an average load in theformer case, or is a comparison temperature in the second case. Forexample, an inference can be made about the duration of the power outagefrom the deviation of the currently measured temperature from thecomparison temperature, which deviation results from the cooling of theelectronic control device of the refrigerant compressor or the coolingof the refrigerant compressor itself.

Therefore, in an especially preferred embodiment of the method accordingto the invention it is provided that

-   -   the electronic control device of the refrigerant compressor        monitors to determine if a power supply of the electronic        control device has been interrupted,    -   and the special cooling cycle is initiated if both an exceeding        or falling short of the comparison parameter by the currently        measured parameter value and a preceding power outage are        detected.

Likewise, said advantageous method is also achieved in an electroniccontrol device according to the invention in that

the electronic control device is configured

-   -   to detect a power outage and    -   to initiate a special cooling cycle, if both an exceeding or        falling short of the comparison parameter by the currently        measured parameter and a preceding power outage have been        detected.

In an especially preferred embodiment of the electronic control deviceaccording to the invention it is provided that the temperature measuringdevice is a component of the electronic control device of therefrigerant compressor or that the temperature measuring device isdisposed on a housing of the refrigerant compressor, in order to be ableto determine an operating temperature of the electronic control deviceof the refrigerant compressor or of the refrigerant compressor.

Normally, the electronic control device of the refrigerant compressoralready comprises a temperature measuring device for other purposes, forexample for monitoring the temperature of the electronic control deviceto prevent overheating, so that the electronic control device does notbecome more expensive due to implementation of this aspect of theinvention and the measured values of said temperature measuring devicecan be employed as the additional temperature according to theinvention.

An additional advantage of the use of the measured values of atemperature measuring device already provided in a traditionalelectronic control device as the additional measured temperature lies inthe fact that only the programming of the electronic control device ofthe refrigerant compressor needs to be altered and not the structure ofthe electronic control device itself. In this way, refrigerantcompressors already in use can be easily adapted for carrying out themethod according to the invention.

Likewise, it is provided in a second especially preferred embodiment ofthe invention that the additional temperature is measured by atemperature measuring device and the temperature measuring device ismounted on a housing of the refrigerant compressor. Since therefrigerant compressor and electronic control device of the refrigerantcompressor are usually manufactured as a module and are supplied to themanufacturer of a refrigeration system, the functioning of the methodaccording to the invention can also be ensured when the temperaturemeasuring device is disposed on the housing of the refrigerantcompressor. Thereby, the temperature measuring device is a part of thesupplied module and the functionality of the method is guaranteed to beindependent of any assembly or connection errors of the manufacturer ofthe refrigeration system. Especially preferably, the temperaturemeasuring device is disposed on an outer side of the housing, while thecomponents of the refrigerant compressor, thus at least the electricdrive unit and the piston-cylinder unit, are disposed within the housingof the refrigerant compressor.

In order to enable the detection of a special operating state in asimple way on the basis of a change of the current operating state ofthe refrigerant compressor without having to rely on a stored comparisonparameter that was predefined in the as-supplied state and stored in thecontrol device of the refrigerant compressor, in another preferredembodiment of the method according to the invention it is provided thatthe at least one measured current parameter value is stored as thestored parameter value in the electronic control device of therefrigerant compressor over at least two operating cycles. This allows aspecial operating state to be inferred from the development of thestored parameter values. Preferably, the stored parameter values arestored over 3, 4, 5, 8, or 10 operating cycles in order to be able tomonitor and model the operating behavior as accurately as possible.

If the currently measured parameter value is the additional temperature,the measured additional temperature can, for example, be stored at thestart of the cooling cycle and/or the measured additional temperaturecan be stored at the end of the cooling cycle. For example, a coolingrate can be determined via the stored temperatures at the beginning of acooling cycle and/or at the end of a cooling cycle, via which rate anexpected additional temperature is determined at the start of the nextcooling cycle, wherein the expected additional temperature is defined asthe comparison temperature, optionally while employing a multiplicativedeviation factor.

Thus, it is advantageous if the comparison parameter is not predefinedas a fixed value in the electronic control device of the refrigerantcompressor, but rather is continuously modified in dependence on anextreme value, thus a maximum value or a minimum value, of the storedparameter values, possibly taking into account a multiplicativedeviation factor. It is also conceivable that the extreme value of thestored parameter values is determined and used directly as comparisonparameter. Therefore, in an especially preferred embodiment of theinvention it is provided that an extreme value of the stored parametervalues in the electronic control device of the refrigerant compressor isselected and the comparison parameter is determined in dependence on theextreme value of the stored parameter values, preferably it correspondsto the extreme value.

Instead of the extreme value, an average value of the stored parametervalues is also suitable for the most accurate modelling and monitoringof the operating behavior of the refrigerant compressor. The averagevalue can be calculated, for example, as the geometric, arithmetic, orharmonic mean value of the stored parameter values. Also, the comparisonvalue can be continuously modified in dependence on the average value,for example taking into account a multiplicative deviation factor.Likewise, it is again conceivable that the average value of the storedparameter values is determined and used directly as comparisonparameter.

For example, the current load or the current average load and/or thecurrent duration of the rest cycle and/or the measured additionaltemperature can be compared with the corresponding extreme values and/oraverage values determined from the stored parameter values in order tobe able to infer reliably that a special operating state has occurredand correspondingly to initiate the special cooling cycle.

Here it should be seen as particularly advantageous that the comparisonparameter can take into account possible variations of the operatingstate in that a predefined deviation factor stored in the electroniccontrol device of the refrigerant compressor is multiplied by theextreme value or the average value in order to define the comparisonparameter. Thus, operation-related variations in the current parametervalues do not initiate a special cooling cycle. Therefore, in anotherespecially preferred embodiment it is provided that the comparisonparameter is determined by multiplying the extreme value or the averagevalue by a deviation factor, wherein the deviation factor is at least1.25, preferably at least 1.50, especially preferably 1.75, especially2.0.

According to the prior art, the preset rotary speed control can beconfigured so that a new starting rotary speed for the next coolingcycle can be set in dependence on the rotary speed behavior of a currentoperating cycle, for example the maximum rotary speed or average rotaryspeed. If the special operating state is not detected and thus a specialcooling cycle cannot be initiated, but rather, a normal cooling cyclefollows the special operating state, the long duration of said coolingcycle and the high rotary speed will also have a negative effect on thefollowing operating cycles: The increased cooling demand results solelyfrom the effects of the special operating state and not from afundamentally higher cold demand of the cooled volume. Nonetheless,according to the preset rotary speed control, the rotary speed of thenext cooling cycle will be increased so that the refrigerant compressoris not driven in an energy optimized way. The higher the average rotaryspeed was in the cooling cycle following the special operating state,the larger the number of cooling cycles that must be run through beforethe rotary speed has adjusted to the required rotary speed. Since,however, a detection of the special operating state takes placeaccording to the invention, said disadvantage of the prior art can beovercome in that the special cooling cycle is not taken into account inthe setting of the starting rotary speed of the next cooling cycle afterthe special cooling cycle, rather, it is set to a starting rotary speedsetting from the last completed cooling cycle that is stored in theelectronic control device. Therefore, in an especially preferredembodiment of the invention it is provided that a starting rotary speedof the refrigerant compressor is set to a value stored in the electroniccontrol device for the cooling cycle following the special coolingcycle.

An especially effective cooling of the cooled volume as a response to aspecial operating state like a defrost operation or power outage isachieved in another embodiment of the invention in that the refrigerantcompressor is operated during the special cooling cycle so that a higheraverage cooling output is supplied to the cooled volume than in acomparable cooling cycle controlled in accordance with the preset rotaryspeed control. The increased cooling output is achieved through anincreased rotary speed of the refrigerant compressor.

A preferred embodiment of the method according to the invention callsfor the refrigerant compressor to be operated during the special coolingcycle so that the rotary speed does not go below a defined rotary speeduntil the end of the special cooling cycle, wherein the defined rotaryspeed is at least 75%, preferably at least 85%, especially preferably atleast 90%, in particular between 95% and 100%, of a maximum rotary speedof the refrigerant compressor. A high value of the defined rotary speed,which is to be understood as a minimum rotary speed, with respect to themaximum rotary speed of the refrigerant compressor, ensures theprovision of a high cooling capacity or cooling output by therefrigerant compressor. Here, the refrigerant compressor can beoperated, for example, at a first defined rotary speed of 95% of themaximum rotary speed over a first defined time period [and] at a seconddefined rotary speed of 80% of the maximum rotary speed over a seconddefined time period, wherein the cycles repeat alternatingly until thespecial cooling cycle ends.

In order to be able to lower the temperature of the cooled volume thatwas raised because of the special operating state as promptly aspossible, thus to be able to produce a high cooling output immediatelyafter the detection of the special operating state, it is provided inanother embodiment of the invention that the refrigerant compressor isaccelerated to a predefined rotary speed at the beginning of the specialcooling cycle, wherein the at least one defined rotary speed is at least70%, more preferably at least 80%, especially preferably at least 90%,in particular between 95% and 100% of a maximum rotary speed of therefrigerant compressor.

The object stated at the start is also solved by a module comprising

-   -   a variable-speed refrigerant compressor having an electric drive        unit and a piston-cylinder unit that can be driven by the        electric drive unit for compression of refrigerant;    -   an electronic control device in accordance with the invention        for control of the cyclic operation of the variable-speed        refrigerant compressor according to a method according to the        invention. Such a module can be easily installed in a        refrigeration system without a control unit of the refrigeration        system transmitting a control signal or a rotary speed setting        to the electronic control device of the refrigerant compressor.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in more detail by means ofembodiment examples. The drawings are merely examples and are intendedto present the ideas of the invention, but not to limit it in any way orto reproduce it conclusively.

Here:

FIG. 1 shows a schematic representation of the back of a refrigerationsystem;

FIG. 2 shows a schematic representation of a refrigerant compressor withanother embodiment of the electronic control device;

FIG. 3 shows a schematic representation of the rotary speed behavior ofthree different cycles of the refrigerant compressor in a preset rotaryspeed control;

FIG. 4 shows a schematic representation of the rotary speed behaviorafter a defrost operation according to the preset rotary speed controlper the prior art;

FIG. 5 shows a schematic representation of the rotary speed behaviorafter a defrost operation according a first embodiment of the methodaccording to the invention;

FIG. 6 shows a schematic representation of the rotary speed behaviorafter a defrost operation according to a second embodiment of the methodaccording to the invention;

FIG. 7 shows a schematic representation of the rotary speed behaviorafter a power outage according to a third embodiment of the methodaccording to the invention.

WAYS OF IMPLEMENTING THE INVENTION

FIG. 1 shows a simple refrigeration system 1 with a variable-speedrefrigerant compressor 2, a refrigerant line 5, and an evaporator 5 a.Refrigerant compressor 2, refrigerant line 5, and evaporator 5 a form aclosed refrigerant system in which refrigerant circulates during theoperation, thus during a cooling cycle C_(K) of the refrigerantcompressor 2. The refrigeration system 1 has a cooled volume 4, whereinheat can be removed or cooling output delivered by the evaporator 5 a byevaporating the refrigerant in evaporator 5 a.

The individual components of the refrigerant compressor 2, thus at leastone piston-cylinder unit in which the refrigerant is cyclicallycompressed and an electric drive unit, via which the piston-cylinderunit can be driven, are disposed within a housing 8 of the refrigerantcompressor 2. The variable-speed refrigerant compressor 2 additionallyhas an electronic control device 6 for control of the rotary speedbehavior of the refrigerant compressor 2, which is connected to theelectric drive unit and controls it. In order to enable of the coolingof the cooled volume 4 to be as energy optimized as possible, theelectronic control device 6 of the variable-speed refrigerant compressor2 operates during the cooling cycle C_(K) according to a programmedsetting, which controls the rotary speed behavior C_(K) of therefrigerant compressor 2 during a cooling cycle C_(K). This presetrotary speed control enables the variable-speed refrigerant compressor 2to be operated in the simple refrigeration system 1 and at the same timeensures operation is as energy optimized as possible. The programmedsetting in this case is already implemented in the programming of theelectronic control device 6 of the refrigerant compressor andrepresents, so to say, a standardized as-delivered state, which enablesoperation to be as energy optimized as possible in a large number ofstandard conditions of use. Usually, the variable-speed refrigerantcompressor 2 and the electronic control device 6 are assembled as amodule by a refrigerant compressor manufacturer and sold as a unit tothe manufacturer of refrigeration systems.

The method according to the invention or the electronic control deviceof the refrigerant compressor according to the invention for adjustingthe operation of the refrigerant compressor to special operating states,which require a high cooling output of the refrigerant compressor 2, isdescribed in detail below.

The refrigeration system 1 does not itself have an autonomous controlunit that can make available switching signals, characteristicparameters, and measured parameters available to the control device 6 ofthe refrigerant compressor 2 or that transmits a control signal thatcontains a rotary speed setting. The only switching signal that thesimple refrigeration system 1 transmits to the control device 6 of therefrigerant compressor 2 derives from a thermostat 3 as a function ofthe temperature level of the cooled volume 4. For this, the thermostat 3as a rule has a temperature sensor, for example a bimetallic strip or avapor pressure-based measurement element or an NTC (negative temperaturecoefficient) element, which is disposed in the cooled volume 4 in orderto measure the temperature of the cooled volume 4 directly, or isdisposed on the evaporator 5 a in order to determine the temperature ofthe cooled volume 4 indirectly. Preferably, the thermostat 3 is designedas a vapor pressure-based bellows thermostat. The thermostat 3 isdesigned to trigger a switching signal, which is transmitted to thecontrol device 6 of the refrigerant compressor 2, or to transmit aswitching signal to the control device 6, which switching signal setsthe refrigerant compressor 2 to an ON state, in which the drive unit isactivated and refrigerant is compressed in the piston-cylinder unit. Thethermostat 3 is designed to trigger an additional switching signal,which is transmitted to the control device 6 in order to transmit anadditional switching signal to the control device 6, which additionalswitching signal sets the refrigerant compressor 2 to an OFF state inwhich the piston-cylinder unit is not subject to any drive torque.

According to one aspect of the invention, a temperature measuring unit 7is provided, via which an additional temperature T_(w) that isindependent of the temperature of the cooled volume 4 is measured. Inthis embodiment, the temperature measuring unit 7 is made as a componentof the control device 6, for example as an onboard sensor on a circuitboard of the control device 6.

FIG. 2 shows a second embodiment of the invention, in which thetemperature measuring unit 7 is mounted on the housing 8 of therefrigerant compressor 2. The housing 8 of the refrigerant compressor 2can be, for example, a hermetically sealable housing 8, which comprisesa lower housing section 8 a and an upper housing section 8 b. In thisembodiment example, the temperature measuring unit 7 is mounted on anouter surface of the upper housing part 8 b. The reference numbers 7′and 7″ designate alternative attachment positions, shown as dashedlines, on an outer side of the housing lower part 8 a, whereas thereference number 7′″ designates an alternative attachment position,represented as a dashed line, on a support leg of the refrigerantcompressor 2.

Functioning of the Invention

A method for operating the variable-speed refrigerant compressor 2 in asimple refrigeration system 1, as is already known from the prior art,is described below by means of FIG. 3. In particular, the control of therotary speed behavior of the variable-speed refrigerant compressor 2,the so-called preset rotary speed control, in which the rotary speedbehavior of the refrigerant compressor 2 is controlled on the basis ofat least one predefined parameter K_(v), which is stored in theelectronic control device 6 of the refrigerant compressor 2, during acooling cycle C_(K), and the at least one parameter value K_(v) ismonitored with respect to its being exceeded and/or fallen short of by acurrent parameter K_(a) of a current cooling cycle C_(Ka).

In this embodiment example, the at least one predefined parameter K_(v)is the duration of a cooling cycle C_(K). Here, the current running timeand the actual duration of the cooling cycle C_(K) are monitored by theelectronic control device 6.

FIG. 3 shows, as an example, three operating cycles C₁, C₂, C₃, whichrepresent different rotary speed behaviors of the variable-speedrefrigerant compressor 2 that can be set during its operation. Anoperating cycle C is composed in each case of a rest cycle C_(R) and acooling cycle C_(K), wherein the refrigerant compressor 2 is inoperation during a cooling cycle C_(K) and force-circulates refrigerantthrough the refrigeration system to cool the cooled volume 4. On theother hand, in the rest cycle C_(R), the refrigerant compressor 2 is notdriven and essentially no cooling of the cooled volume 4 takes place.

The first cooling cycle C_(K1) is begun at time t₁ by the switchingsignal triggered by the thermostat 3, wherein the refrigerant compressor2 is set to an ON state by the electronic control device 6. Thethermostat 3 triggers the switching signal when a deviation of thetemperature level of the cooled volume 4 from a preset temperature levelis detected, which indicates a cooling demand in the cooled volume 4, sothat cooling output can be sent to the cooled volume 4 by therefrigerant compressor 2. In this case, an exceeding of the presettemperature level is detected by thermostat 3 or by the temperaturefeeler of thermostat 3 at time t₁. The temperature in the cooled volume4 is thus too high. As soon as the variable-speed refrigerant compressor2 is set to the ON state, it is operated at a starting rotary speed v₁.At time t₂, which corresponds to the predefined duration of the coolingcycle C_(K1), the preset temperature level in the cooled volume 4 hasnot yet been reached, and the thermostat 3 accordingly has not triggereda switching signal to set the refrigerant compressor 2 to the OFF state.

Thus, a further cooling requirement exists in the cooled volume 4 attime t₂. Since the actual cooling requirement of the cooled volume 4 isnot known to the electronic control device 6, the rotary speed v isincreased by a preset value, for example 10%, 20%, 30%, or 50%, of thecurrent rotary speed v₁, to a first increased rotary speed v₂. Thisensures that the cold demand in the cooled volume 4 can be recoveredfaster, or if the cold demand is generally very high, or the coolingcycle C_(K) can be quickly ended.

At time t₃, which corresponds to a limit value of a data record storedin the predefined running time K_(v), the cold demand of the cooledvolume 4 has still not yet been satisfied, so that in this example, anadditional increase of the rotary speed v to a second increased rotaryspeed v₃ takes place for the reasons given above.

At time t₄, the electronic control device 6 receives the additionalswitching signal triggered by the thermostat 3, which signals that thecold demand in the cooled volume 4 has been satisfied and thetemperature in the cooled volume 4 lies within the predefinedtemperature level needed for cooling. On the basis of the additionalswitching signal, the electronic control device 6 sets the refrigerantcompressor 2 to the OFF state, so that the second rest cycle C_(R2) isinitiated. The time that has passed between times t₁ and t₄ correspondsto the actual duration K₁ of the first cooling cycle C_(K1). Since theactual duration K₁ is greater than the predefined duration K_(v), it canbe provided either that the next cooling cycle C_(K2) is begun withoutchange in accordance with the preset rotary speed control, with the riskthat it must be readjusted as in C_(K1), or it can be provided that theelectronic control device 6 starts from an increased cold demand in thenext cooling cycle C_(K2). The latter can be the case in particular whencooling cycles C_(K) whose duration was longer than the predefinedrunning time K_(v) already exist before the cooling cycle C_(K1).

In order to take care of the expected higher cold demand of the cooledvolume 4 and to be able to provide it within the predefined durationK_(v) of the next cooling cycle C_(K2), the next cooling cycle C_(K2),which again is triggered by the switching signal, will be operated at anincreased starting rotary speed v₄. The increased starting rotary speedv₄ can, for example, correspond to the last rotary speed v of thepreceding cooling cycle C_(K1) or can be calculated as the average valueof the rotary speeds v₁, v₂, v₃ of the preceding cooling cycle C_(K1).

In the second cooling cycle C_(K2), the electronic control device 6receives an additional switching signal triggered by the thermostat 3 toswitch off the refrigerant compressor 2 at time t₆. The actual durationK₂ of the second cooling cycle C_(K2) is, however, less than thepredefined duration K_(v), so that the actual cooling demand of thecooled volume 4 has already been satisfied before the predefinedduration K_(v) is reached at time t₇. From this, the electronic controldevice 6 can infer that a lower cooling demand is necessary in the nextcooling cycle C_(K3).

In order to take care of the expected lower cooling demand of the cooledvolume 4 and to reach it within the predefined duration K_(v) of thenext cooling cycle C_(K3), the third cooling cycle C_(K3) is startedwith a rotary speed v that is lower than the rotary speed v₄ of thepreceding cooling cycle C_(K2), the lower rotary speed v in thisembodiment example corresponding to the starting rotary speed v₁. In thethird cooling cycle C_(K3), the predefined duration K_(v) correspondswith the duration K₃ of the third cooling cycle C₃, so that the coolingdemand of the cooled volume 4 is reached with the rotary speed v₁ withinthe predefined duration K_(v). In the third cooling cycle C_(K3), anespecially energy-conserving operation of the refrigerant compressor 2is achieved.

The above described control of the rotary speed behavior of therefrigerant compressor 2 in the electronic control device 6 correspondsto the preset rotary speed control, which is configured to enableoperation that is as energy optimized as possible over the entireoperating time of the refrigerant compressor 2.

In the case of simple refrigeration systems 1 with automatic defrosting,the refrigeration system 1 carries out a defrost operation at preset, asa rule periodic, intervals. During the defrost operation the evaporator5 a is heated, for example via heating elements provided for this, inorder to remove layers of frost or ice that have built up in the cooledvolume 4 in the region of the evaporator 5 a. In this case, at least therefrigerant in the evaporator 5 a also becomes heated. The defrostoperation is initiated in a rest cycle C_(R), so that the refrigerantcompressor 2 is in the OFF state during the defrost operation. Duringthe defrost operation, a switching signal that sets the refrigerantcompressor 2 to the ON state is not triggered by the thermostat 3. Onlyafter the end of the defrost operation does the thermostat 3 trigger theswitching signal, so that the refrigerant compressor 2 is set to the ONstate by the electronic control device 6 of the refrigerant compressor2.

The disadvantages of the prior art are explained by means of the rotaryspeed behavior depicted in FIG. 4. The first two cooling cycles C_(K1),C_(K2) run according to the preset rotary speed control, as describedabove. For the sake of simplicity, the two cooling cycles C_(K1), C_(K2)are shown as operating cycles in which the predefined duration K_(v)corresponds to the actual duration K₁, K₂, and the refrigerantcompressor 2 is operated at the rotary speed v₁. A defrost operation,indicated as DEFROST in the figure, is initiated during the third restcycle C_(R3), which follows the second cooling cycle C_(K2).

After the end of the defrost operation, the thermostat 3 triggers theswitching signal and the refrigerant compressor 2 is set to the ONstate. Since the electronic control device 6 of the refrigerantcompressor 2 does not receive a control signal from the simplerefrigeration system 1 that allows it to infer that a defrost cycle hastaken place, the rotary speed behavior of the refrigerant compressor 2is controlled via the preset rotary speed control, and a third coolingcycle C_(K3) is begun. Said cooling cycle starts with the startingrotary speed v₁. As soon as the running time exceeds the predefinedduration K_(v), the rotary speed v of the refrigerant compressor 2 israised to the first increased rotary speed v₂. Since the actual durationof the third cooling cycle C_(K3) also exceeds the limit values of thepredefined duration K_(v1), K_(v2), K_(v3), the rotary speed v isincreased stepwise to the increased rotary speeds v₃, v₄, and finally toa maximum rotary speed v_(max). Only after the third limit value hasexceeded the predefined duration K_(v3) is the maximum rotary speedv_(max), at which the refrigerant compressor 2 produces the maximumcooling output, reached in this embodiment example. The cooling demandof the cooled volume 4 of the refrigeration system 1, which hasincreased because of the defrost operation, is thus not reached afterthe preset rotary speed control according to the prior art has run. Inthis way, on the one hand, the temperature level in the cooled volume,which has increased because of the defrost operation, is not reduced toa lower temperature level in a timely way with the full cooling outputof the refrigerant compressor 2.

Another disadvantage is seen in the previously described setting of astarting rotary speed v_(s) for the next cooling cycle C_(K4) in thethird cooling cycle C_(K3). Since the maximum rotary speed v_(max) isreached and the predefined duration K_(v) is clearly exceeded by thecurrent duration K₃ of the third cooling cycle C_(K3), the startingrotary speed v_(s) of the fourth cooling cycle C_(K4) is greatlyincreased over the starting rotary speed v₁ of the third cooling cycleC_(K3) in accordance with the preset rotary speed control. While theincrease of the starting rotary speed v_(s) of the next cooling cycleC_(K) because of increased cooling demand in the cooled volume 4 as arule leads to an operation that is as energy optimized as possible, therefrigerant compressor 2 in the case described above will be operated ata rotary speed that is too high for the cooling demand of the cooledvolume 4.

According to the invention, therefore, at least one comparison parameterP_(v) is stored in the electronic control device 6 of the refrigerantcompressor 2, and an exceeding or falling short of the comparisonparameter P_(v) by a current parameter value P_(a) is monitored in orderto detect a preceding defrost operation. In the embodiment example shownin FIG. 5, the comparison parameter is a comparison duration P_(v) ofthe rest cycle C_(R). For this reason, monitoring to determine if thecurrent duration P_(a) of the current rest cycle C_(R) exceeds thecomparison duration P_(v) is continuously carried out. As soon as anexceeding of the comparison duration P_(v) is detected, a cooling cycleC_(K) will be not be started upon reception of the switching signaltriggered by the thermostat 3, but rather a special cooling cycle C_(D)that differs from the preset rotary speed control will be initiated.

Since the rotary speed behavior in the special cooling cycle C_(D) iscontrolled according to parameters stored in the electronic controldevice 6 of the refrigerant compressor 2, it is possible to operate therefrigerant compressor 2 at a high rotary speed v immediately after theend of the defrost operation, in this case already at the maximum rotaryspeed v_(max). Thus, as a direct result of the defrost operation, a highcooling output, in particular a maximum cooling output, is madeavailable by the refrigerant compressor in order to reduce thetemperature level of the cooled volume 4 as fast as possible. Throughthis, on the one hand, the duration of the special cooling cycle C_(D)is reduced by comparison with the duration of the cooling cycle C_(K3)conducted according to the preset rotary speed control (see FIG. 3), andon the other hand, the energy consumption is also lowered through this.It can, for example, be provided that the rotary speed v is keptconstant during the entire special cooling cycle C_(D), as shown by thesolid rotary speed curve in FIG. 5. However, it can also be providedthat the refrigerant compressor 2 is operated with a rotary speedbehavior like the dashed speed curve illustrates during the specialcooling cycle C_(D). In this example variation, the refrigerantcompressor 2 is driven at the maximum rotary speed v_(max) over theduration C_(D1) and then driven at the third elevated rotary speed v₄over the duration C_(D2), before the refrigerant compressor 2 has beenaccelerated back to the maximum rotary speed v_(max). Basically, anyprogressive, regressive, or stepwise paths of the speed curve during thespecial cooling cycle C_(D) are conceivable.

In this embodiment example, the starting rotary speed v_(s) of thefollowing third cooling cycle C_(K3) is not affected by the rotary speedbehavior during the special cooling cycle C_(D), rather, the refrigerantcompressor 2 is operated in the following third cooling cycle C_(K3) atthe rotary speed v₁ specified for it in the second cooling cycle C_(K2),since the special cooling cycle C_(D) is not taken into consideration inestablishing the starting rotary speed v_(s) of the following thirdcooling cycle C_(K3).

FIG. 6 shows a second embodiment variation of the method according tothe invention. While the duration of the rest cycle C_(R) functioned asa comparison parameter P_(v) in the previously discussed embodimentexample, in this embodiment example, an average load L_(m) of therefrigerant compressor 2 in a starting phase of the cooling cycle C_(K)serves as the comparison parameter P_(v) (not shown). Here, the load Lof the refrigerant compressor 2 is determined by measuring the electriccurrent through the refrigerant compressor 2, in particular the electriccurrent flowing through the electric drive unit of the refrigerantcompressor 2. After the end of the defrost operation, which again isindicated as DEFROST, a cooling cycle C_(K) controlled by the presetrotary speed control is started. During the starting phase of thecooling cycle C_(K), in this example during the first 50 s after therefrigerant compressor 2 was set to the ON state, the current load L iscontinuously measured and a current average load L_(m) is calculatedover the duration of the starting phase of the cooling cycle C_(K). Thiscurrent average load L_(m) is, as the currently measured parameter valueP_(a), then compared with the comparison parameter P_(v) stored in theelectronic control device 6 of the refrigerant compressor 2. Since thecurrently measured average load L_(m) exceeds the stored comparisonparameter P_(v) because of the heating of the refrigerant in theevaporator 5 a during the defrost operation and/or because of the highcooling demand of the cooled volume 4, and the electronic control device6 thus infers that a defrost operation has taken place, the coolingcycle C_(K) is interrupted after the end of the starting phase and thespecial cooling cycle C_(D) is started. Since the load L can only bemeasured each time during the cooling cycle C_(K), the special coolingcycle C_(D) cannot be started directly on the basis of the switchingsignal triggered by the thermostat 3, but rather only after the end ofthe starting phase of the cooling cycle C_(K). However, a comparisonwith the rotary speed behavior in FIG. 4 clearly shows that therefrigerant compressor 2 in this embodiment variation also promptlymakes available a high cooling output after the defrost operation, inthis case even the maximum cooling output, and the cooled spacetemperature is accordingly reduced to a lower temperature level faster.

FIG. 7 shows another aspect of the invention, in which, because of themonitoring of the comparison parameter P_(v) by the electronic controldevice 6 of the refrigerant compressor 2 for an interruption of thepower supply that has occurred (indicated as POWER BREAK in thedrawing), the special cooling cycle C_(D) is initiated. In order to beable to infer a preceding power outage, the electronic control device 6monitors the current supply of the refrigerant compressor 2 and thusdetects a current outage. However, this information by itself is notenough to make an inference about the initiation of the special coolingcycle C_(D), since the electronic control device 6 does not have anyinformation about the duration of the power outage. In the case of ashort power outage, the initiation of the special cooling cycle C_(D) isnot purposeful, since the cooled volume temperature will only negligiblyrise during the outage. However, if the current interruption lastslonger, the cooled volume 4 will become heated and should be rapidlycooled down by means of the special cooling cycle C_(D).

Therefore, in the electronic control device 6, besides the power outage,the additional temperature T_(w) is employed as a currently measuredparameter value P_(a), wherein the additional temperature T_(w), asshown in FIGS. 1 and 2, is measured by a temperature measuring device 7,which is either an integral component of the electronic control device 6of the refrigerant compressor 2 or is disposed on the housing 8 of therefrigerant compressor 2. In this embodiment example, the comparisonparameter P_(v) is a comparison temperature T_(v), with which thecurrently measured additional temperature T_(w) is compared.

How much the electronic control device 6 or the housing 8 of therefrigerant compressor 2 has cooled can be tested by comparing thecurrently measured additional temperature T_(w) with the comparisontemperature T_(v). During the normal operation, in which the electroniccontrol device 6 and housing 8 become heated during the cooling cycleC_(K), only a partial cooling takes place in the rest cycle C_(R) beforethe next cooling cycle C_(K) is initiated. If the currently measuredadditional temperature T_(w) therefore is below the comparisontemperature T_(v), it can be inferred from this that a cooling cycleC_(K) has not taken place over a period of time that is longer thanaverage. Because of the information that, on the one hand, a poweroutage has taken place and, on the other hand, no cooling cycle C_(K)has taken place over an above-average period of time, the specialcooling cycle C_(D) will be initiated by the electronic control device 6of the refrigerant compressor 2, since it can be inferred that a lengthypower outage has occurred.

For the sake of clarity, one is referred to the description of FIG. 5for the details of the special cooling cycle C_(D). It goes withoutsaying here that a plurality of parameters can also be monitored at thesame time, thus the duration of the rest cycle C_(R) and/or the averageload L_(m) and/or the additional temperature T_(w).

It can be provided in alternative embodiment variations of the inventionthat the additional temperature T_(w) functions as the currentlymeasured parameter value P_(a) and the comparison parameter P_(v) is acomparison temperature T_(v), and upon the detection of a deviation ofthe currently measured additional temperature T_(w) from the comparisontemperature T_(v), a special cooling cycle C_(D) is initiated without apower outage having been detected at the same time, thus in other wordsa preceding defrost operation can be inferred from the monitoring of theadditional temperature T_(w), and the corresponding special coolingcycle C_(D) can be initiated. Likewise, it is conceivable that a specialcooling cycle C_(D) will be initiated if the currently measuredparameter P_(a) is not the additional temperature T_(w) and a precedingpower outage was detected by the electronic control device 6 of therefrigerant compressor 2. For example, a long power outage can beinferred if the currently measured parameter value P_(a) is thecurrently measured load L or the currently determined average load L_(m)and an exceeding or falling short of the comparison parameter P_(v) wasdetected.

Basically, it can be provided in any of the described embodimentvariations that the refrigerant compressor 2 is not driven constantly atthe maximum rotary speed v_(max) during the special cooling cycle C_(D),but rather at a percentage of said rotary speed, for example at 85% ofthe maximum rotary speed v_(max). It can further be advantageous if therefrigerant compressor 2 does not exceed a predefined rotary speed v_(D)during the special cooling cycle C_(D), wherein the predefined rotaryspeed v_(D) is again defined as a percentage of the maximum rotary speedv_(max), for example 75%. It is also advantageous if the refrigerantcompressor 2 is operated at a high predefined rotary speed v_(D)immediately after the initiation of the special cooling cycle C_(D),wherein the predefined v_(D) is, for example, 92% of the maximum rotaryspeed v_(max).

In order to be able to detect the detection [sic] of special operatingstates better and more reliably, it can be provided in any of thepreviously described embodiment variations that the currently measuredparameter values P_(a) are stored in the electronic control device 6 ofthe refrigerant compressor 2 over a plurality of operating cycles C.This is especially advantageous if the value of the comparison parameterP_(V) is adjusted on the basis of the stored parameter values P_(S). Forinstance, the comparison parameter P_(V) can, for example, be varied independence on an extreme value P_(E), thus a minimum or maximum, of thestored parameter values P_(S) or, for example, in dependence on anaverage value P_(M). The comparison parameter P_(V) can correspondeither directly to the extreme value P_(E) or to the average valueP_(M). However, it is advantageous if a multiplicative deviation factor,for example a factor of 1.5, is taken into account in setting thecomparison parameter P_(V), thus the extreme value P_(E) or the averagevalue P_(M) is multiplied by the deviation factor in order to set thevalue of the comparison parameter P_(V). If the stored parameter valuesP_(S) change during operation, the comparison parameter P_(V) will beautomatically adjusted.

REFERENCE NUMBERS

-   1 Refrigeration system-   2 Refrigerant compressor-   3 Thermostat-   4 Cooled volume-   5 Cooling line    -   5 a Evaporator-   6 Electronic control device of refrigerant compressor 2-   7 Temperature measuring device-   8 Housing of refrigerant compressor 2    -   8 a Lower housing section    -   8 b Upper housing section-   K_(v) Predefined parameter-   K_(a) Current parameter-   v Rotary speed-   C_(R) Rest cycle-   C_(K) Cooling cycle-   C Operating cycle

What is claimed is:
 1. A method for operation of a rotary speed-variablerefrigerant compressor for cooling a cooled volume of a refrigerationsystem, wherein it comprises a thermostat for direct or indirectmonitoring of a temperature state of the cooled volume and where therefrigerant compressor is operated cyclically, and a cooling cycle(C_(K)) of the refrigerant compressor begins when the refrigerantcompressor is set into an ON state by a switching signal triggered by athermostat, and the cooling cycle (C_(K)) ends when the refrigerantcompressor is set to an OFF state by an additional signal triggered bythe thermostat, where an operating cycle (C) comprises, besides thecooling cycle (C_(K)), a rest cycle (C_(R)) following the cooling cycle(C_(K)), and where the rotary speed behavior of the refrigeratorcompressor is controlled during a cooling cycle (C_(K)) by means of apreset rotary speed control stored in an electronic control device ofthe refrigerant compressor, wherein at least one comparison parameter(P_(V)) is stored in the electronic control device of the refrigerantcompressor and an exceeding or falling short of the comparison parameter(P_(V)) by a currently measured parameter value (P_(a)) is monitored, aspecial cooling cycle (C_(D)) that is different from the preset rotaryspeed control is initiated if the current measured parameter value(P_(a)) exceeds or falls short of the comparison parameter (P_(V)),optionally, a current cooling cycle (C_(K)) that is controlled by thepreset rotary speed control is interrupted by the special cooling cycle(C_(D)).
 2. The method as in claim 1, wherein the at least one monitoredcomparison parameter (P_(V)) or one of the monitored comparisonparameters (P_(V)) is a load (L) of the refrigerant compressor in astarting phase of a cooling cycle (C_(K)).
 3. The method as in claim 2,wherein the load (L) is monitored as the average load (L_(m)), averagedover the duration of the starting phase.
 4. The method as in claim 1,wherein the at least one monitored comparison parameter (P_(V)) or oneof the monitored comparison parameters (P_(V)) is a duration of the restcycle (C_(R)).
 5. The method as in claim 1, wherein an additionaltemperature (T_(w)) that is independent of the temperature of the cooledvolume is measured, the currently measured parameter value (P_(a)) orone of the currently measured parameter values (P_(a)) is the additionaltemperature (T_(w)), the at least one monitored comparison parameter(P_(V)) or one of the monitored comparison parameters (P_(V)) is acomparison temperature (T_(V)).
 6. The method as in claim 1, wherein theelectronic control device of the refrigerant compressor monitors to seeif a power supply of the electronic control device has been interrupted,and the special cooling cycle (C_(D)) is initiated if both an exceedingor falling short of the comparison parameter (P_(V)) by the currentlymeasured parameter value (P_(a)) and a preceding interruption of thepower supply are detected.
 7. The method as in claim 1, wherein the atleast one measured current parameter value (P_(a)) is stored in theelectronic control device of the refrigerant compressor over at leasttwo operating cycles (C) as stored parameter value (P_(S)).
 8. Themethod as in claim 7, wherein an extreme value (P_(E)) of the storedparameter values (P_(S)) is selected in the electronic control device ofthe refrigerant compressor and the comparison parameter (P_(V)) isdetermined in dependence on the extreme value (P_(E)).
 9. The method asin claim 7, wherein an average value (P_(M)) of the stored parametervalues (P_(S)) is calculated in the electronic control device of therefrigerant compressor and the comparison parameter (P_(V)) isdetermined in dependence on the average value (P_(M)).
 10. The method asin claim 8, wherein the comparison parameter (P_(V)) is determined bymultiplying the extreme value (P_(E)) or the average value (P_(M)) by adeviation factor, wherein the deviation factor is at least 1.25.
 11. Themethod as in claim 1, wherein a starting rotary speed (v_(s)) of therefrigerant compressor is established for the cooling cycle (C_(K))following the special cooling cycle (C_(C)) [sic; C_(D)] on the basis ofa value stored in the electronic control device.
 12. The method as inclaim 1, wherein the refrigerant compressor is operated during thespecial cooling cycle (C_(D)) so that a higher average cooling capacityis sent to the cooled volume than in the case of a comparable coolingcycle controlled in accordance with the preset rotary speed control(C_(K)).
 13. The method as in claim 1, wherein the refrigerantcompressor is operated during the special cooling cycle (C_(D)) so thata defined rotary speed (v_(c)) is not exceeded before the end of thespecial cooling cycle (C_(D)), wherein the defined rotary speed (v_(c))is at least 75%, of a maximum rotary speed of the refrigerantcompressor.
 14. The method as in claim 1, wherein the refrigerantcompressor is accelerated at the beginning of the special cooling cycle(C_(D)) to a predefined rotary speed (v_(c)), wherein the at least onedefined rotary speed (v_(c)) is at least 70%, of a maximum rotary speedof the refrigerant compressor.
 15. An electronic control device forcontrol of the cyclic operation of a rotary speed-variable refrigerantcompressor, where the electronic control device is configured to switchthe refrigerant compressor on due to a switching signal triggered by athermostat for direct or indirect monitoring of a temperature state of acooled volume of a refrigeration system in order to begin a coolingcycle (C_(K)) and to end a rest cycle (C_(R)), and to switch therefrigerant compressor off again on the basis of an additional switchingsignal triggered by the thermostat in order to end the cooling cycle(C_(K)) and to begin a rest cycle (C_(R)), and to control the rotaryspeed behavior of the refrigerant compressor during a cooling cycle(C_(K)) by means of a preset rotary speed control stored in theelectronic control device, wherein at least one comparison parameter(P_(V)) is stored in the electronic control device and the electroniccontrol device is configured to detect an exceeding or falling short ofthe comparison parameter (P_(V)) by a current measured parameter value(P_(a)), to initiate a special cooling cycle (C_(D)) that is differentfrom the preset rotary speed control if the current measured parametervalue (P_(a)) exceeds or falls short of the comparison parameter(P_(V)), optionally to interrupt a current cooling cycle ( ) [sic;(C_(K))] controlled by the preset rotary speed control in order to startthe special cooling cycle ( ) [sic; (C_(D))].
 16. The electronic controldevice as in claim 15, wherein the electronic control device isconfigured to measure a load of the refrigerant compressor as thecurrent through the refrigerant compressor and that the storedcomparison parameter (P_(v)) and the currently measured parameter value(P_(a)) are loads.
 17. The electronic control device as in claim 15,wherein the electronic control device is configured to determine aduration of the rest cycle (C_(R)) and that the stored comparisonparameter (P_(v)) and the currently measured parameter value (P_(a)) arethe duration of a rest cycle (C_(R)).
 18. The electronic control deviceas in claim 15, wherein the electronic control device is connected to atemperature measuring device for measurement of an additionaltemperature (T_(w)) that is independent of the temperature of the cooledvolume, and that the stored comparison parameter (P_(v)) is a comparisontemperature (T_(v)) and the currently measured parameter value (P_(a))is the additional temperature (T_(w)).
 19. The electronic control deviceas in claim 18, wherein the temperature measuring device is a componentof the electronic control device of the refrigerant compressor or thatthe temperature measuring device is disposed on a housing of therefrigerant compressor.
 20. The electronic control device as in claim15, wherein the electronic control device is configured to detect aninterruption of the power supply and to initiate a special cooling cycle(C_(D)) if both an exceeding or falling short of the comparisonparameter (P_(V)) by the currently measured parameter value (P_(a)) anda preceding interruption of the power supply were detected.
 21. A modulecomprising a rotary speed-variable refrigerant compressor with anelectric drive unit and a piston-cylinder unit that can be driven by theelectric drive unit for compression of refrigerant; an electroniccontrol device as in claim 15 for control of the cyclic operation of therotary speed-variable refrigerant compressor.
 22. The method as in claim3, wherein the duration of the starting phase is between 10 s and 90 s.23. The method as in claim 22, wherein the duration of the startingphase is between 40 s and 70 s.
 24. The method as in claim 8, whereinthe comparison parameter (P_(V)) is determined in dependence on theextreme value (P_(E)), which corresponds to a maximum value of theextreme value (P_(E)).
 25. The method as in claim 9, wherein thecomparison parameter (P_(V)) is determined in dependence on the averagevalue (P_(M)), which corresponds to the average value (P_(M)).
 26. Themethod as in claim 10, wherein the deviation factor is at least 1.50.27. The method as in claim 26, wherein the deviation factor is 1.75. 28.The method as in claim 26, wherein the deviation factor is 2.0.
 29. Themethod as in claim 13, wherein the defined rotary speed (v_(c)) is atleast 85% of a maximum rotary speed of the refrigerant compressor. 30.The method as in claim 29, wherein the defined rotary speed (v_(c)) isat least 90% of a maximum rotary speed of the refrigerant compressor.31. The method as in claim 30, wherein the defined rotary speed (v_(c))is between 95% and 100% of a maximum rotary speed of the refrigerantcompressor.
 32. The method as in claim 14, wherein the at least onedefined rotary speed (v_(c)) is more than at least 80% of a maximumrotary speed of the refrigerant compressor.
 33. The method as in claim32, wherein the at least one defined rotary speed (v_(c)) is at least90% of a maximum rotary speed of the refrigerant compressor.
 34. Themethod as in claim 33, wherein the at least one defined rotary speed(v_(c)) is between 95% and 100% of a maximum rotary speed of therefrigerant compressor.
 35. A module comprising a rotary speed-variablerefrigerant compressor with an electric drive unit and a piston-cylinderunit that can be driven by the electric drive unit for compression ofrefrigerant; an electronic control device for control of the cyclicoperation of the rotary speed-variable refrigerant compressor as in themethod of claim 1.